1. Field of the Invention
The present invention relates generally to flame-retardant fibers and nonwoven fabrics formed of such fibers, and more particularly to flame-retardant fibers which form no dioxin-related compounds when burned, and nonwoven fabrics, woven fabrics and formed products made up of such fibers.
2. Prior Art
Synthetic fibers such as those formed of nylon, polyester, polypropylene and the like, because of being excellent in physical and chemical properties, find now wide applications in the form of clothing, curtain, carpet and other materials. However, these fibers are combustible; so they are required to have flame retardancy when applied to automotive trims, housing, etc.
Imparting flame retardancy to fibers is generally achieved by adding flame retardants to the starting polymers or post-treating fibers with flame retardants.
A typical example of a polymer with a flame-retardant added thereto is a polyolefinic composite fiber mixed with a fine particle form of flame-retardant which has a decomposition temperature higher than its spinning temperature by at least 100.degree. C., as disclosed in Japanese Patent Laid-Open No. 58(1983)-156019.
Another typical composite fiber based on polyester is disclosed in Japanese Patent Laid-Open No. 54(1979)-134120, which comprises a polyester component containing phosphorus and/or a halogen and a fiber-forming polyester component.
Among known flame retardants that may be added to the starting polymer, there is decabromodiphenyl oxide that has the merit of imparting sufficient flame retardancy to the polymer in a small amount, so that the resultant fiber can be best made of the property of the polymer of its own, but has the demerit of forming dioxin-related compounds when burned. Since the dioxin-related compounds are known to be of carcinogenicity, it is expected that the use of decabromodiphenyl oxide will be banned in the near future.
Other flame retardants (for instance, tricresyl phosphate, ammonium phosphate and aluminum hydroxide) having such a structure that inhibits the formation of dioxin-related substances must be added to the starting polymer at an increased concentration to impart sufficient flame retardancy to the polymer. Thus these agents have the disadvantage of making the physical properties of the polymer fiber worse unless added thereto in a sufficient amount, and so incurring some considerable expense.
For the post-treatment of fibers with a flame retardant, the flame retardant diluted with water or an organic solvent is deposited to the fibers or fabrics by impregnation or spraying. For instance, Japanese Patent Laid-Open No. 48(1973)-13696 discloses a thermoplastic resin fiber sprayed with an organic halogen type of flame retardant containing phosphorus. With such a method, it is relatively easy to make fibers or fabrics flame-retardant. However, a problem with this method is that the flame retardant detaches itself off the surfaces of the fibers in a powder form or becomes readily disengaged from the fibers by washing.
An object of the present invention is therefore to achieve provision at low costs of high-quality fibers which form no dioxin-related compound even when burned and maintains the required flame retardancy even when the amount of the flame retardant used is small.